Reverse Shallow Trench Isolation Process

ABSTRACT

A method of polishing a substrate surface containing silicon nitride and silicon oxide or silicon dioxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, or both, and 3) water, wherein at 2 psi downpressure the silicon nitride removal rate is at least 500 angstroms per minute and the selectivity of silicon nitride to silicon oxide is at least 30.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/956,232 filed 16 Aug. 2007.

BACKGROUND OF THE INVENTION

The present invention is directed to a process of making ashallow-trench-isolation type structure comprising polishing a siliconnitride layer disposed over a silicon dioxide or silicon oxide filmformed for example from tetraethoxysilane (TEOS) or plasma enhancedtetraethoxysilane (PETEOS) using an aqueous chemical mechanicalplanarization slurry comprising, or alternatively consisting essentiallyof or consisting of: 1) hydrous (not calcined) ceria abrasive; 2) aneffective amount of vinyl pyridine polymers and/or copolymers, e.g.,poly(4-vinylpyridine), poly(4-vinylpyridine co-styrene), or mixturethereof; and 3) a pH adjusting agent which is advantageously an alkylammonium hydroxide.

Classical shallow trench isolation (STI) is a well-known method in thefabrication of IC chips. U.S. Pat. No. 6,342,432 describes manufacturinga traditional shallow trench isolation wherein shallow trenches areetched in the substrate and an oxide liner is thermally grown on thetrench walls. The trench is then filled with an insulating material. Atypical method of trench formation comprises initially growing a padoxide layer on the substrate, and depositing a nitride polish stop layerthereon. A photoresist mask is then applied to define the trench areas.The exposed portions of the nitride layer are then etched away, followedby the pad oxide layer. The etching continues into the substrate to formthe shallow trench. When etching of the trench is completed, thephotoresist is stripped off the nitride layer. Next, the substrate isoxidized to form an oxide liner on the walls and base of the trench tocontrol the silicon-silicon dioxide interface quality. The trench isthen filled with an insulating material (or “trench fill”), such assilicon dioxide derived from TEOS. The surface is then planarized toprovide a flat surface at the trench edges, as by chemical-mechanicalpolishing (CMP) to the nitride polish stop, and the nitride and padoxide are stripped off the active areas to complete the trench isolationstructure. Disadvantageously, during planarization, an excess amount ofthe trench fill tends to be removed, resulting in the top of the trenchfill being “dished” in the middle; i.e., lower than the top of thetrench. This condition complicates subsequent processing, therebylowering manufacturing yield and increasing production costs.

A typical STI process is shown in FIGS. 1A to 1F. To prevent dishing,conventional STI formation methodologies include the formation of anadditional photolithographic mask, known as a planarization mask. Asshown in FIG. 1A, a trench 100 a is formed in a semiconductor substrate100 after deposition of a pad oxide layer 105 and a nitride polish stoplayer 110.An oxide liner 115 is then thermally grown, and trench 100 ais filled with an insulating material 120 (typically silicon oxide).Insulating material 120 is then polished, as by CMP, to obtain a flatupper surface, as shown in FIG. 1B. The portion of insulating material120 above trench 100 a is masked by photoresist mask 125 (see FIG. 1C),then the portions of insulating material 120 unprotected by mask 125 areetched, as shown in FIG. 1D. Mask 125 is then removed, and insulatingmaterial 120 is further polished, as by CMP, down to the level of polishstop layer 110 (see FIG. 1E). The silicon nitride layer has served as astopping layer during the chemical-mechanical planarization process, asthe overall polishing rate has decreased upon exposure of the siliconnitride layer. In this application, a high TEOS to silicon nitrideselectivity was required for successful planarization. A typical goalwas to achieve high TEOS removal rates (e.g., 1500 A/min to 2500 A/min)and stop at Si₃N₄ (e.g., less than 20 A/min) at low polishing pressure,providing a high TEOS/Si₃N₄ (greater than 5, typically greater than 10,often greater than 20) selectivity during polishing. When the siliconnitride layer is exposed, the largest area of the substrate exposed tothe chemical-mechanical polishing system comprises silicon nitride.While this silicon nitride can be removed by etching, removing thesilicon nitride layer by polishing to achieve a highly planar anduniform surface is desirable. After the silicon nitride polish stop 110is removed, the trench fill 120 is above the top of trench 100, as shownin FIG. 1F. The amount of the protrusion may be very small. Evenmoderately selective polishing compositions, having a selectivity ofbetween 4 and 25, more typically between 6 and 12, will result inconsiderable erosion of the protruding oxide.

However, as oxide line widths have become smaller in next-generationdevices, in some circumstances it is desirable to utilize polishingsystems having selectivity for silicon nitride over oxide polishing, inorder to minimize defectivity in the oxide lines formed on the substratesurface. Several chemical-mechanical polishing compositions forsubstrates containing low dielectric constant materials (e.g., oxide)are known. Generally, prior art utilizes ceria abrasive to obtain a highsilicon dioxide to silicon nitride polishing ratio (selectivity).

Conversely to get high silicon nitride to silicon dioxide ratios, theprior art slurries use an abrasive such as alumina, titania, and silica.U.S. Pat. No. 6,043,155 discloses a cerium oxide-based slurry forinorganic and organic insulating films, having selectivity for silicondioxide versus silicon nitride polishing. U.S. Patent ApplicationPublication 2002/0168857 A1 discloses a method for manufacturing asemiconductor device in which silicon dioxide is deposited on a siliconnitride film patterned with trenches, and a two-stagechemical-mechanical polishing process is then performed to selectivelyremove overlying silicon dioxide, thus leaving trenches filled withsilicon dioxide. Thus, there remains a need in the art for polishingcompositions and methods having the reverse selectivity, for selectivelyremoving silicon nitride over underlying dielectric components. U.S.Patent Application Publication 2006/0099814 teaches a slurry containingceria at a pH of about 7 or less, with examples having pH values of 4.9,and shows a silicon nitride to oxide selectivity of less than 25. U.S.Patent Application Publication 2006/0108326 teaches a slurry containingceria and shows a silicon nitride to oxide selectivity of less than 25.What is needed is a silicon nitride to silicon oxide selectivity ofgreater than 30, preferably greater than 40, is needed, where thepolishing rate of the silicon nitride must simultaneously be useful,e.g., above 500 angstroms per minute.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a process of making ashallow-trench-isolation type structure comprising polishing a siliconnitride layer disposed over a silicon dioxide or silicon oxide filmformed for example from TEOS or PETEOS using an aqueous chemicalmechanical planarization slurry comprising, or alternatively consistingessentially of or consisting of: 1) hydrous (not calcined) ceriaabrasive; 2) an effective amount of vinyl pyridine polymers and/orcopolymers, e.g., poly(4-vinylpyridine), poly(4-vinylpyridineco-styrene), or mixture thereof; and 3) a pH adjusting agent which isadvantageously an alkyl ammonium hydroxide.

The invention includes the use of poly(4-vinylpyridine) and poly(4-vinylpyridine co-styrene) for suppressing the TEOS rate with no effect on theremoval rate of silicon nitride. Hence poly(4-vinylpyridine) andcopolymers of 4-vinylpyridine such as poly 4-vinyl pyridineco-polystyrene are selective with respect to silicon nitride withcomplete suppression of oxide removal rate. The homopolymer andcopolymer offer different protection profiles, and a polishingcomposition most preferably has both poly(4-vinylpyridine) and one ormore copolymers of 4-vinylpyridine such as poly(4-vinyl pyridineco-styrene). However, the invention has additional improvements on theart. The invention is robust such that while removal rates are tunablethe amount of material needed to affect tenability is sufficiently large(a difference of at least 50 ppm from high silicon nitride to siliconoxide selectivity to low silicon nitride to silicon selectivity) and thecomposition provides high polishing rates with low downpressure. Whilethe system allows excellent tenability over a considerable range,advantageously the silicon nitride to silicon oxide selectivity ispreferably at least 30, more preferably at least 35, most preferably atleast 40. At pH 3.9 to 4.1, the selectivity of silicon nitride tosilicon oxide can exceed 40, and can even be made to exceed 60 or 80. Atsuch high selectivities, the small protruding silicon oxide layerremaining after STI will not be damaged, and can be made thinner thanwould be possible if the slurry had a selectivity of 25 or less,especially 10 or less. At the same time, advantageously, by onlychanging the amount of vinyl pyridine-based polymers, the selectivity ofsilicon nitride to silicon oxide can be made equal to 1 (0.8 to 1.2,preferably 0.9 to 1.1). This allows use of the base slurry in a varietyof manufacturing variants where a slurry that always polishes siliconnitride at rates greater than silicon oxide can not be used.

The polishing composition advantageously comprises, consists essentiallyof, or consists of: A) about 0.05% to 2%, preferably 0.2% to 1%, byweight of hydrous ceria; B) about 10 to 1000, preferably about 20 toabout 600, more than 50 to about 300 ppm, or 60 to 200 ppm, or 80 to 150ppm, of one or more of poly(4-vinylpyridine), a polymer made frommonomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridineco-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof;C) a carrier which is preferably high purity water; D) optionally a pHadjuster, preferably a halide-free ammonium-based compound such as antetra-alkyl ammonium compound, to adjust the pH between 3.5 and 4.5,preferably between 3.8 and 4.2, if necessary; and E) optionally between5 and 500 ppm of nonionic surfactants including for example Zonyl FSJ®(10 to 1000 ppm) and Zonyl FSN® (5 to 50 ppm) to reduce defect countsand increase slurry stability.

Zonyl FSN®: it is a non-ionic surfactant, and a mixture of telomericmonoether with polyethylene glycol of formulaR_(f)CH₂CH₂O(CH₂CH₂O)_(x)H: Where R_(f)═F(CF₂CF₂)_(y), x=0 to about 25,and y=1 to about 9. The structures of Zonyl FSJ®, an anionic phosphatefluorosurfactant, is R_(f)(CH₂CH₂O)_(x) P(O)(ONH₄)_(y), whereR_(f)═F(CF₂CF₂)_(z), x=1 or 2, y=2 or 1, x+y=3, and z=1 to about 7. Thepolishing method comprises movably contacting a substrate comprising asurface having both silicon nitride and silicon oxide with a polishingpad and with a polishing composition of this invention disposed betweenthe polishing pad and the substrate surface. Advantageously the pH orthe polishing composition is between 3.5 and 4.5, more particularlybetween 3.8 and 3.9, between 3.9 and 3.99, 4.00, or between 4.01 and4.1.

Preferred compositions have 60 or more ppm, for example 70 ppm, 80 ppm,90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, or 150 ppm ofpoly(4-vinylpyridine). Most preferred are polishing compositions having80 to 150 ppm of poly(4-vinylpyridine) or a copolymer containing atleast 70 molar percent of 4-vinylpyridine copolymerized with otherpolymers.

The invention includes a method of polishing a substrate surfacecontaining silicon nitride and silicon oxide or silicon dioxide,comprising movably contacting the surface with a polishing pad andhaving a polishing composition disposed between the polishing pad andthe surface, said polishing composition comprising 1) hydrous ceriaabrasive; 2) an effective amount of polyvinylpyridine, vinyl pyridinecopolymers having more than 60 molar percent of monomers being vinylpyridine, or both, and 3) water. Advantageously the polishingcomposition comprises at least 60 ppm, preferably at least 80 ppm, forexample between 100 and 200 ppm of poly(4-vinylpyridine). In anotherembodiment the polishing composition comprises poly(4-vinylpyridineco-styrene). Advantageously the silicon nitride to silicon oxideselectivity is at least 30, and the silicon nitride removal rate is atleast 500 angstroms per minute. More advantageously, the silicon nitrideto silicon oxide selectivity is at least 40, and the silicon nitrideremoval rate is at least 600 angstroms per minute when polished at a 2psi downpressure. In a preferred embodiment the silicon nitride tosilicon oxide selectivity is at least 60. Typically the polishingcomposition is at pH 3.9 to 4.1. The composition is tunable.Advantageously, the silicon nitride to silicon oxide selectivity isvariable from 0.8 to over 50 by changing only the amount ofpolyvinylpyridine, vinyl pyridine copolymers, or both present in thepolishing composition. In a preferred embodiment the polishingcomposition comprises 1) about 0.05% to 2% by weight of hydrous ceria;2) more than 50 to about 300 ppm of one or more ofpoly(4-vinylpyridine), a polymer made from monomers consistingessentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other4-vinylpyridine-based copolymers, or mixture thereof; and 3) water.Alternatively the polishing composition comprises 1) about 0.05% to 2%by weight of hydrous ceria; 2) 80 to about 600 ppm of one or more ofpoly(4-vinylpyridine), a polymer made from monomers consistingessentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other4-vinylpyridine-based copolymers, or mixture thereof; and 3) high puritywater, wherein the pH is between 3.5 and 4.5. In a very preferredembodiment, the polishing composition consists essentially of 1) about0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppmpoly(4-vinylpyridine); and 3) high purity water, and a pH adjuster sothat the pH is between 3.8 and 4.2. Advantageously the polishingcomposition consists essentially of 1) about 0.05% to 2% by weight ofhydrous ceria; 2) 80 to about 600 ppm of a copolymer containing at least70 molar percent of 4-vinylpyridine copolymerized with other polymers,poly(4-vinylpyridine), or mixture thereof; and 3) high purity water.

The invention also includes a method of polishing a substrate surfacecontaining silicon nitride and silicon oxide such as silicon dioxide,said method comprising movably contacting the surface with a polishingpad and having a polishing composition disposed between the polishingpad and the surface, said polishing composition comprising 1) hydrousceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, orboth, and 3) water, wherein at 2 psi downpressure the silicon nitrideremoval rate is at least 500 angstroms per minute and the selectivity ofsilicon nitride to silicon oxide is at least 30, preferably at least 40at 2 psi downpressure. Preferably the hydrous ceria was provided bymilling submicron ceria in an aqueous milling medium of no high purityalpha alumina at a pH of between 10 and 11 for a time sufficient toallow the hydroxyl ions to react with the surface of the ceria.Advantageously the polishing composition contains substantially nopolydiallyldimethylammonium halide, poly(amidoamine),poly(methacryloyloxyethyltrimethylammonium) chloride,poly(methacryloyloxyethyldimethylbenzylammonium) chloride,poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), andcopolymers of acrylamide and diallyldimethylammonium chloride; and/or nono oxidizing agents; and/or less than 20 ppm total of chloride andfluoride. The above polymers can cause coagulation of the slurry. Thepolishing composition may additionally comprise between 0.005% and 0.1%of an ethoxylated fluorosurfactant to further reduce defects.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A to 1E shows an STI manufacturing process where compositions ofthis invention could be usefully employed.

DETAILED DESCRIPTION OF THE INVENTION

The invention includes a polishing composition having greater than 20ppm of a vinyl pyridine homopolymer or a vinyl pyridine copolymer, orboth, used with hydrous ceria (preferably of 100 to 200 nanometersdiameter) that allows a silicon nitride to silicon oxide (a term knownin the art to indicate a material formed for example from TEOS)selectivity of less than 1 to greater than 30, preferably greater than40, where the polishing rate of the silicon nitride is economicallyuseful, e.g., above 500 angstroms per minute, preferably above 600angstroms per minute, more preferably over 700 angstroms per minute at 2psi downpressure. Different selectivities will doubtless be observedbetween silicon nitride and other dielectric materials such as silicondioxide and against conductors such as polysilicon.

In preferred embodiments the polymer in the polishing compositioncomprises, consists essentially of, or consists of poly(4-vinylpyridineco-styrene). In another preferred embodiment the polymer in thepolishing composition comprises, consists essentially of, or consists ofpoly(4-vinylpyridine co-styrene). Advantageously the molar ratio ofvinyl pyridine to styrene in the copolymer is at least 50:50, morepreferably at least 60:40. In another embodiment, the polymer in thepolishing composition comprises, consists essentially of, or consists ofcopolymers of 4-vinylpyridine and other monomers, where advantageouslythe copolymers have greater than 50 molar percent, preferably greaterthan 60 molar percent, of the polymer being 4-vinylpyridine.

The use of hydrous, as opposed to calcined or “pure” ceria, is criticalto the invention. By hydrous we mean for example a ceria formed by forexample a precipitation process, which preferably has not undergoneheated drying in an air atmosphere at a temperature sufficient to driveoff water, or exposure to strong oxidizing agents, or other processwhich results in a similar product. Even better, ceria milled in anaqueous liquid at pH 9-11 for a sufficient period of time is mosthydrous and is preferred. Ceria formed by pyrogenic methods are notdesired. Calcined ceria is similarly not preferred. In preferredembodiments, the composition comprises less than 0.2%, preferably lessthan 0.05%, and most preferably is free of any or each of 1) ceriaformed pyrogenically; 2) calcined ceria; 3) ceria that has undergoneheated drying in an air atmosphere at a temperature sufficient to driveoff water; and 4) ceria that has undergone exposure to strong oxidizingagents such as ceria formed by oxidizing soluble cerium salts, unlessany of the above has been subsequently treated to revert the ceria to ahydrous form. Hydrous ceria is very active against silicon oxide andsilicon dioxide. One method of potentially identifying hydrous ceria isthat, in the absence of polymer, the polishing rate of silicon oxide issubstantially greater than the polishing rate of silicon nitride at pH3.9 to 4.5. As we have tested only a limited number of ceria products,however, the above is no guarantee that the ceria is hydrous.

A method of providing the hydrous ceria includes milling the ceria at ahigh pH of between 10 and 11 in a milling medium of no high purity alphaalumina for a time sufficient to allow the hydroxyl ions to react withthe surface of the ceria, such that in a low pH environment the ceria ishydrous.

Advantageously the ceria has a particle size between 50 and 300nanometers, with about 100 to about 200 nanometers diameter beingpreferred, and 130 to 170 nanometers being most preferred.

A useful commercially available ceria is such as is described in U.S.Pat. No. 6,238,450. The ceria maintains a positive ionic surface chargeat pH values of about 4 to a pH of 10, and the ceria agglomeratedparticles have been subjected to a mechano-chemical treatment whichcomprises milling a slurry of the particles using low-purity alumina orzirconia milling media at a pH of from 9 to 12.5, until an essentiallyde-agglomerated product with a BET surface area of at least 10 m²/gm isobtained. The pH at which the de-agglomeration occurs is preferably from10 to 12.5 and the time required may be from seconds up to 15 daysdepending on the equipment used and the degree of de-agglomerationrequired. Conventional vibratory mills such as a Sweco mill may requireseven days or more.

Another potentially useful ceria might be obtained following the processof U.S. Pat. No. 4,661,330 which discloses a method for preparing highsurface area and high purity ceria. Ammonium ceria nitrate is refluxedfor 24 hours with ammonium sulfate to obtain a hydrous ceria powder.This powder, provided it can be milled to a average particle size below0.2 microns, is likely useful. In that patent, the hydrous ceria wassubsequently calcinated at 538° C. in air to form ceria having a surfacearea of 150 m²/g. After calcining, the ceria would not be useful inpreferred variants of this invention.

The 4-vinylpyridine-based polymers of the present invention, whenpresent in amounts up to 100 ppm, have substantially no detrimentaleffect on the silicon nitride polishing rate. By substantially nodetrimental effect we mean the silicon nitride polishing rate is greaterthan about 50% of the comparative silicon nitrate removal rate whenpolishing under identical parameters with a slurry devoid of the vinylpyridine-based polymers. The poly(4-vinylpyridine) andpoly(4-vinylpyridine co-styrene) have a low affinity to the siliconnitride. Therefore, the presence of this polymer does not radicallyaffect the polishing rate of the silicon nitride.

In contrast, the data in Table 1 of U.S. Patent Application Publication2006/0099814 and 2006/0108326 show that polyethyleneimine in amounts ofas little as 10 ppm results not only in a large reduction in the amountof oxide but also over a 95% reduction in the silicon nitride removalrate. It is difficult to manufacture and use polishing compositionswhere a variation of a few ppm will drastically affect the systemperformance. Absorption or reaction of the polymers during shipping andstorage, and during mixing and storage in a plant, can result in a lossof a few ppm of such surface-active material, resulting in undesirableand significant variations in slurry performance. Even withpolyvinylpyridine, tests for particle size distribution showed thepolymer was coating the Accusizer™sensors. Preferably the polishingcomposition has substantially no, e.g., less than 10 ppm, morepreferably less than 1 ppm, most preferably zero ppm, of polymers suchas polyethyleneimine. Preferably the polishing composition has little,e.g., less than 10 ppm, more preferably less than 1 ppm, most preferablyzero ppm, of polymers such as polydiallyldimethylammonium halide,poly(amidoamine), poly(methacryloyloxyethyltrimethylammonium) chloride,poly(methacryloyloxyethyldimethylbenzylammonium) chloride,poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), andcopolymers of acrylamide and diallyldimethylammonium chloride. The abovepolymers can cause coagulation of the slurry.

The combination of vinyl pyridine-based polymers and copolymers, inamounts greater than 20 ppm, preferably greater than 40 ppm, and oftenmore than 60 ppm, in combination with the hydrous ceria allows siliconnitride to silicon oxide (e.g., from TEOS or PETEOS) selectivity to be25 or more, preferably 30 or more, more preferably 40 or more, whilestill maintaining a silicon nitride removal rate of 400 angstroms perminute or more, preferably 600 to 1500 angstroms per minute, mostpreferably 800 to 1000 angstroms per minute at 2 psi downpressure.Generally, polishing rates increase with increasing down pressure. At 4psi downpressure, which is not recommended as it is very high andsubstrate damage will be more frequent, about a 2× increase in removalrates may be realized. Nevertheless the desirable silicon nitride tosilicon oxide selectivity of greater than 30, preferably greater than40, can be maintained.

In compositions having normal (calcined) ceria, in the absence ofpolymers, generally the silicon nitride to silicon dioxide selectivityis near 1.5, and the selectivity of silicon nitride to silicon oxide isbetween 1.5 and 2. Using hydrous ceria, however, in the absence ofpolymers, the silicon nitride to silicon dioxide selectivity is below0.4. Adding the polymer changes this selectivity to above 25. Thereforethe compositions of this invention are tunable for silicon nitride tosilicon oxide selectivity from 0.4 to above 30, while at the same timemaintaining silicon nitride rates of over 600 angstroms per minute andwhich do not vary by more than about 50% over the range ofselectivities. The compositions of this invention, most importantly, aretunable to a nitride to oxide selectivity of about 1. This is highlydesirable in the industry.

Advantageously the compositions of this invention have little (less than0.1%) or no oxidizing agents, including peroxides and the like.

Advantageously in one embodiment the compositions of this invention havelittle (less than 20 ppm, more preferably less than 5 ppm) or nohalides, especially chloride and fluoride. Such halides may damagecertain low k dielectric materials. If acid is needed, for example toobtain the proper pH, the acid should contain an anion such as sulfate.

Various corrosion reducing agents can be added. Such agents typicallybind to copper and reduce corrosion. However, because the composition ofthis invention has no oxidizers, such corrosion reducing agents aretypically not needed or desired.

Non-ionic surfactants, including particularly between 0.005% and 0.1% ofan acetylenic alcohol comprising at least two hydroxyl substituents,more particularly the Zonyl™ type acetylenic diol surfactants which mayor may not have an ethoxylated portion, are useful to reduce defects.

The polishing composition optionally can further comprise a biocide. Thebiocide can be any suitable biocide, for example an isothiazolinonebiocide. The amount of biocide used in the polishing compositiontypically is about 1 ppm to about 500 ppm, and preferably is about 10ppm to about 200 ppm.

The polishing composition also can be provided as a concentrate which isintended to be diluted with an appropriate amount of water prior to use.In such an embodiment, the polishing composition concentrate cancomprise the hydrous ceria abrasive, the 4-vinyl pyridine-basedhomopolymer or copolymer, a base or other appropriate pH adjustingagent, and water in amounts such that, upon dilution of the concentratewith an appropriate amount of water, each component of the polishingcomposition will be present in the polishing composition in an amountwithin the appropriate range recited above for each component. Theconcentrate may contain an amount that is about 2 times (or about 3times, about 4 times, or about 5 times) greater than the concentrationrecited above for each component so that, when the concentrate isdiluted with an equal volume of water (e.g., 2 equal volumes water, 3equal volumes of water, or 4 equal volumes of water, . . . ), eachcomponent will be present in the polishing composition in an amountwithin the ranges set forth above for each component.

EXAMPLES

In the examples, the following components and suppliers were used.Colloidal silica Syton® OX-K was obtained from DuPont Air ProductsNanoMaterials L.L.C., Tempe, Ariz., or Mirrasol®-30180 was obtained fromPrecision C, LLC, 102 Old Mill Road, Cartersville, Ga. 30120. Ceria(calcined) was obtained from Baikowski Japan, Co., Ltd, 6-17-13Higashinarashino Chiba, JP 275-001. Ceria (hydrous) was obtained fromSaint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615

As used herein, silicon oxide or the dielectric “oxide” layer is formedfrom deposition of tetraethoxy silane or tetraethyl orthosilicate(TEOS), more particularly plasma enhanced deposition of tetraethoxysilane (PETEOS). Other compounds and methods are available to formsimilar silicon oxide layers. As used herein, “A/min” is angstrom(s) perminute. Back pressure and down force is provided in pounds per squareinch (psi) units. Platen rotational speed of polishing tool is providedin rpm (revolution(s) per minute). Slurry flow is provided inmilliliters per minute (ml/min). Reported removal rates of TEOS andsilicon nitride are those observed at 2 psi down pressure. While largerrates are obtainable at higher down pressure, down pressures in excessof 3 psi are discouraged. Removal rates at 2 psi down pressure areadvantageously 500 A/min to 800 A/min for Si₃N₄ and less than 20 A/minfor oxide.

In the examples, the polishing pad used during CMP was Politex® andIC1000 obtained from Rodel, Inc, Phoenix, Ariz. Oxide wafers were 15,000A PETEOS on silicon. Silicon nitride blanket wafers were 10,000 A Si₃N₄on silicon on silicon, and were obtained from Silicon ValleyMicroelectronics, 1150 Campbell Ave, Calif., 95126. The CMP tool thatwas used is a Mirra®, manufactured by Applied Materials, 3050 BoweresAvenue, Santa Clara, Calif., 95054. A Rodel Politex® embossed pad,supplied by Rodel, Inc, 3804 East Watkins Street, Phoenix, Ariz., 85034,was used on the platen for the blanket wafer polishing studies. Padswere broken-in by polishing twenty-five dummy oxide (deposited by plasmaenhanced CVD from a TEOS precursor, PETEOS) wafers. In order to qualifythe tool settings and the pad break-in, two PETEOS monitors werepolished with Syton® OX-K colloidal silica, supplied by DuPont AirProducts NanoMaterials L.L.C., at baseline conditions.

In blanket wafers studies, groupings were made to simulate successivefilm removal: Si₃N₄ and PETEOS. The tool mid-point conditions were:table speed; 123 rpm, head speed; 112 rpm, membrane pressure, 2.0 psi;inter-tube pressure, 0.0 psi; and slurry flow of 200 ml/min.

Comparative Example 1

In a 3-liter beaker, a ceria dispersion (18.26 weight %), purchased fromSaint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615, were addedto deionized water and allowed to stir using a magnetic stirrer for fiveminutes. To this mixture, tetramethylammonium hydroxide (5 wt %solution) was added to bring the final pH to 4.00. Example 2 was thesame as example 1 in table 1, but had 100 PPM of poly(4-vinylpyridine)added. Example 3 was the same as example 1 in table 1, except 100 PPM ofpoly(4-vinylpyridine co-polystyrene) was added. Comparative Example 4was the same as example 2 in table 1, except that ceria particles werereplaced with silica (180 nanometers) particles.

Compositions and polishing data are provided in Table 1.

TABLE 1 Effect of Adding Poly(4-vinylpyridine) and Poly(4-vinylpyridineco-styrene) on Si₃N₄/TEOS selectivity at 2 psi down pressure Exam- Exam-ple #1 Exam- Exam- ple # 4 Sample Control ple # 2 ple # 3 ControlAbrasive, ceria (D = 200 NM) 0.5 0.5 0.5 Abrasive, Silica (D50 = 180 NM)0.5 Poly (4-vinyl pyridine), PPM 0 100 0 100 Poly (4-vinyl pyridine co-0 0 100 0 styrene), PPM Tetramethyl ammonium 05 05 05 05 hydroxide, ,ppm pH 4.0 3.8 3.8 4.0 RR of Silicon nitride (A/min) 809 740 692 37 RRof PETEOS (A/min) 2150 28 57 5 Selectivity (Si₃N₄/PETEOS) 0.4 26 12 7.4

It can be seen that Poly(4-vinyl pyridine) at 100 ppm reduces TEOSremoval to below 30 angstroms per minute (a reduction of over 85%),while reducing the silicon nitride removal rate by less than 20% andallowing a silicon nitride removal rate in excess of 600 angstroms perminute. These parameters are highly desirable in the industry.

The effect of using hydrous ceria is also evident. In compositionshaving normal (calcined) ceria, in the absence of polymers, generallythe silicon nitride to silicon dioxide selectivity is near 1.5, and theselectivity of silicon nitride to silicon oxide is between 1.5 and 2.Using hydrous ceria, however, in the absence of polymers, the siliconnitride to silicon dioxide selectivity is below 0.4. Adding the polymerchanges this selectivity to above 25. Therefore the compositions of thisinvention are tunable for silicon nitride to silicon oxide selectivityfrom 0.4 to above 30, while at the same time maintaining silicon nitriderates of over 600 angstroms per minute and which do not vary by morethan about 50% over the range of selectivities. The compositions of thisinvention, most importantly, are tunable to a nitride to oxideselectivity of about 1. This is highly desirable in the industry.

Example 5

In Example 5 et seq. a slightly different manufacturing method was used.In a 3-liter beaker, a ceria dispersion (18.26 weight %), purchased fromSaint-Gobain Inc., 1 New Bond Street, Worcester, Mass. 01615, was addedto 1 deionized water and allowed to stir using a magnetic stirrer forfive minutes. To this mixture, poly(4-vinyl pyridine) was added during aperiod of 4 minutes, followed by addition of tetramethylammoniumhydroxide to bring the final pH to 4.0. In Examples 5, 6 and 7, theamount of ceria was varied. Polishing data is presented in Table 2.

TABLE 2 Effect of Differing Percent Solid Ceria on Si₃N₄/TEOSselectivity Using Poly(4-vinylpyridine) Sample Example # 5 Example # 6Example 7 Abrasive, ceria (D = 200 NM) 0.5 0.7 1.0 Poly (4-vinylpyridine), PPM 50 50 50 Tetramethyl ammonium 2.73 g 2.79 g 2.85 ghydroxide, pH adjuster, 5% solution pH 4.01 4.00 4.1 RR of Siliconnitride Avg. of 3 710 825 906 runs (A/min) RR of PETEOS Avg. of 3 runs 94.5 5 (A/min) Selectivity Avg. of 3 runs 58 79 181 (Si₃N₄/PETEOS)

Example 8 and comparative example 9 further show the benefit of hydrousceria (from Saint Gobain) versus a calcined ceria (obtained fromBaikowski). Compositional and polishing rate data are presented in Table3.

TABLE 3 Effect of Comparison of 0.5% Ceria Particles on Si₃N₄/TEOSselectivity Example # 8 Example # 9 Sample Saint-Gobain BaikowskiAbrasive, ceria (D = 200 NM) 0.5 0.5 Poly (4-vinyl pyridine), PPM 50 50Tetramethyl ammonium 2.74 g 1.04 g hydroxide pH 4.0 4.03 RR of Siliconnitride Avg. of 3 710 239 runs (A/min) RR of PETEOS Avg. of 3 runs 9 22(A/min) Selectivity (Si₃N₄/PETOS) 79 10

The invention is intended to be limited by the disclosure and/or theclaims, as the law of various jurisdictions proscribe, and is intendedto be illustrated by but is not intended to be limited by the Examples.

1. A method of polishing a substrate surface containing silicon nitrideand silicon oxide, comprising movably contacting the surface with apolishing pad and having a polishing composition disposed between thepolishing pad and the surface, said polishing composition comprising 1)hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymershaving more than 60 molar percent of monomers being vinyl pyridine, orboth, and 3) water, wherein the polishing composition comprises at least60 ppm of poly(4-vinylpyridine).
 2. The method of claim 1 wherein thepolishing composition comprises at least 80 ppm ofpoly(4-vinylpyridine).
 3. The method of claim 1 wherein the polishingcomposition comprises between 100 and 200 ppm of poly(4-vinylpyridine).4. The method of claim 1 wherein the polishing composition comprisespoly(4-vinyl pyridine co-styrene).
 5. The method of claim 1 wherein thesilicon nitride to silicon oxide selectivity is at least 30, and whereinthe silicon nitride removal rate is at least 500 angstroms per minute.6. The method of claim 1 wherein the silicon nitride to silicon oxideselectivity is at least 40, and wherein the silicon nitride removal rateis at least 600 angstroms per minute when polished at a 2 psidownpressure.
 7. The method of claim 1 wherein the silicon nitride tosilicon oxide selectivity is at least
 60. 8. The method of claim 1wherein the polishing composition is at pH 3.9 to 4.1.
 9. The method ofclaim 1 wherein the silicon nitride to silicon oxide selectivity isvariable from 0.8 to over 50 by changing only the amount ofpolyvinylpyridine, vinyl pyridine copolymers, or both present in thepolishing composition.
 10. The method of claim 1 wherein the polishingcomposition comprises 1) about 0.05% to 2% by weight of hydrous ceria;2) more than 60 to about 300 ppm of one or more ofpoly(4-vinylpyridine), a polymer made from monomers consistingessentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other4-vinylpyridine-based copolymers, or mixture thereof; and 3) water. 11.The method of claim 1 wherein the polishing composition comprises 1)about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600 ppm ofone or more of poly(4-vinylpyridine), a polymer made from monomersconsisting essentially of 4-vinylpyridine, poly(4-vinylpyridineco-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof;and 3) high purity water, wherein the pH is between 3.5 and 4.5.
 12. Themethod of claim 1 wherein the polishing composition consists essentiallyof 1) about 0.05% to 2% by weight of hydrous ceria; 2) 80 to about 600ppm poly(4-vinylpyridine); and 3) high purity water, wherein the pH isbetween 3.8 and 4.2.
 13. The method of claim 1 wherein the polishingcomposition consists essentially of 1) about 0.05% to 2% by weight ofhydrous ceria; 2) 80 to about 600 ppm of a copolymer containing at least70 molar percent of 4-vinylpyridine copolymerized with other polymers,poly(4-vinylpyridine), or mixture thereof; and 3) high purity water. 14.A method of polishing a substrate surface containing silicon nitride andsilicon oxide, comprising movably contacting the surface with apolishing pad and having a polishing composition disposed between thepolishing pad and the surface, said polishing composition comprising 1)hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers,or both, and 3) water, wherein at 2 psi downpressure the silicon nitrideremoval rate is at least 500 angstroms per minute and the selectivity ofsilicon nitride to silicon oxide is at least 30 and wherein thepolishing composition comprises at least 60 ppm ofpoly(4-vinylpyridine).
 15. The method of claim 14 wherein theselectivity of silicon nitride to silicon oxide at 2 psi downpressure isat least
 40. 16. The method of claim 15 wherein the hydrous ceria wasprovided by milling submicron ceria in an aqueous milling medium of nohigh purity alpha alumina at a pH of between 10 and 11 for a timesufficient to allow the hydroxyl ions to react with the surface of theceria.
 17. The method of claim 15 wherein the polishing compositioncontains substantially no polydiallyldimethylammonium halide,poly(amidoamine), poly(methacryloyloxyethyltrimethylammonium) chloride,poly(methacryloyloxyethyldimethylbenzylammonium) chloride,poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylamine), andcopolymers of acrylamide and diallyldimethylammonium chloride.
 18. Themethod of claim 15 wherein the polishing composition contains nooxidizing agents.
 19. The method of claim 15 wherein the polishingcomposition contains less than 20 ppm total of chloride and fluoride.20. The method of claim 15 wherein the polishing compositionadditionally comprises between 0.005% and 0.1% of an ethoxylatedfluorosurfactant.